Electrophotographic machines, such as, for example, copiers and printers, produce images by forming a latent image charge pattern on a photoconductive surface. The photoconductive surface carries the latent image through a developing station wherein pigmented toner particles are drawn by electrostatic attraction onto the latent image charge pattern on the photoconductive surface. An electric field is applied to transfer the image from the photoconductive surface onto either an intermediate transfer member or an image substrate, such as, for example, a piece of paper. Thereafter, the image is fixed, such as, for example, by fusing, to the image substrate.
In some electrophotographic machines, the photoconductive surface may be disposed upon a photoconductive member configured as an endless-loop belt having a photoconductive layer or surface. In other electrophotographic machines, the photoconductive surface is disposed on a photoconductive member configured as a cylindrical roller or drum, variously referred to as an image cylinder, photoconductive drum or photoconductive roller. Generally, the photoconductive drum includes an inner roller or mandrel over which a photoconductive sleeve is disposed. The mandrel is typically constructed of aluminum. The photoconductive sleeve is typically constructed from a metal substrate, such as, for example, nickel, onto which several layers of material, including a photoconductive layer, are disposed.
The substrates are typically formed by electroplating, and initially have a very smooth inside and outside surface. In fact, the surfaces are so smooth that an acid etching process is conventionally used to improve adhesion of the photoconductive and/or other layers to the substrate. The acid etching process removes metal oxides from the substrates and thereby desirably increases adhesion of materials to and increases the conductivity of the substrate. However, the acid etching process may increase the surface roughness of the inside and/or outside surfaces of the substrate to an undesirable degree. A substrate having an outer surface that is too rough or which has a roughness in excess of a certain limit can cause the thickness of the photoconductive layer disposed thereon to vary and cause localized differences in the response of the layer to the charging and exposing processes which, in turn, may result in undesirable image artifacts appearing on the image substrate. A substrate having an inside surface that is too rough or which has a roughness in excess of a certain limit may render the photoconductive sleeve less compatible with the air-mounting process by which the sleeves are typically mounted onto a drum or mandrel to thereby assemble the photoconductive drum.
Moreover, acid etching processes are generally not self-limiting and therefore significant process variation can occur. More particularly, the amount of etching that occurs is dependent at least in part upon the concentration of the acid bath, temperature of the bath, time in the bath, and the microcomposition of the nickel substrate. The process variation occurs not only between substrates, i.e., from one substrate to another, but also occurs within a single substrate.
Therefore, what is needed in the art is an improved acid etching process for preparing the surfaces of a substrate to be used as the photoconductive surface of the photoconductive drum in electrophotographic machine.